Pass the XRef-instance explicitly to the StructTreeRoot class

This avoids the current situation where we're accessing it through various dictionaries, since that's a somewhat brittle solution given that in the general case a `Dict`-instance may not have the `xref`-field set (see e.g. the empty-Dict).

src/core/catalog.js

@@ -262,7 +262,7 @@ class Catalog {
   get structTreeRoot() {
     let structTree = null;
     try {
-      structTree = this._readStructTreeRoot();
+      structTree = this.#readStructTreeRoot();
     } catch (ex) {
       if (ex instanceof MissingDataException) {
         throw ex;
@@ -272,17 +272,14 @@ class Catalog {
     return shadow(this, "structTreeRoot", structTree);
   }
 
-  /**
-   * @private
-   */
-  _readStructTreeRoot() {
+  #readStructTreeRoot() {
     const rawObj = this._catDict.getRaw("StructTreeRoot");
     const obj = this.xref.fetchIfRef(rawObj);
     if (!(obj instanceof Dict)) {
       return null;
     }
 
-    const root = new StructTreeRoot(obj, rawObj);
+    const root = new StructTreeRoot(this.xref, obj, rawObj);
     root.init();
     return root;
   }

src/core/struct_tree.js

@@ -29,7 +29,8 @@ const StructElementType = {
 };
 
 class StructTreeRoot {
-  constructor(rootDict, rootRef) {
+  constructor(xref, rootDict, rootRef) {
+    this.xref = xref;
     this.dict = rootDict;
     this.ref = rootRef instanceof Ref ? rootRef : null;
     this.roleMap = new Map();
@@ -158,7 +159,7 @@ class StructTreeRoot {
     }
   }
 
-  async canUpdateStructTree({ pdfManager, xref, newAnnotationsByPage }) {
+  async canUpdateStructTree({ pdfManager, newAnnotationsByPage }) {
     if (!this.ref) {
       warn("Cannot update the struct tree: no root reference.");
       return false;
@@ -180,7 +181,7 @@ class StructTreeRoot {
       warn("Cannot update the struct tree: nums isn't an array.");
       return false;
     }
-    const numberTree = new NumberTree(parentTree, xref);
+    const numberTree = new NumberTree(parentTree, this.xref);
 
     for (const pageIndex of newAnnotationsByPage.keys()) {
       const { pageDict } = await pdfManager.getPage(pageIndex);
@@ -201,7 +202,7 @@ class StructTreeRoot {
       const { pageDict } = await pdfManager.getPage(pageIndex);
       StructTreeRoot.#collectParents({
         elements,
-        xref: this.dict.xref,
+        xref: this.xref,
         pageDict,
         numberTree,
       });
@@ -233,9 +234,8 @@ class StructTreeRoot {
   }
 
   async updateStructureTree({ newAnnotationsByPage, pdfManager, changes }) {
-    const xref = this.dict.xref;
+    const { ref: structTreeRootRef, xref } = this;
     const structTreeRoot = this.dict.clone();
-    const structTreeRootRef = this.ref;
     const cache = new RefSetCache();
     cache.put(structTreeRootRef, structTreeRoot);
 
@@ -541,6 +541,7 @@ class StructTreeRoot {
 class StructElementNode {
   constructor(tree, dict) {
     this.tree = tree;
+    this.xref = tree.xref;
     this.dict = dict;
     this.kids = [];
     this.parseKids();
@@ -565,10 +566,7 @@ class StructElementNode {
     const kids = this.dict.get("K");
     if (Array.isArray(kids)) {
       for (const kid of kids) {
-        const element = this.parseKid(
-          pageObjId,
-          this.dict.xref.fetchIfRef(kid)
-        );
+        const element = this.parseKid(pageObjId, this.xref.fetchIfRef(kid));
         if (element) {
           this.kids.push(element);
         }
@@ -657,7 +655,8 @@ class StructElement {
 class StructTreePage {
   constructor(structTreeRoot, pageDict) {
     this.root = structTreeRoot;
-    this.rootDict = structTreeRoot ? structTreeRoot.dict : null;
+    this.xref = structTreeRoot?.xref ?? null;
+    this.rootDict = structTreeRoot?.dict ?? null;
     this.pageDict = pageDict;
     this.nodes = [];
   }
@@ -683,7 +682,7 @@ class StructTreePage {
     }
 
     const map = new Map();
-    const numberTree = new NumberTree(parentTree, this.rootDict.xref);
+    const numberTree = new NumberTree(parentTree, this.xref);
 
     for (const [elemId] of ids) {
       const obj = numberTree.getRaw(elemId);
@@ -710,14 +709,14 @@ class StructTreePage {
     }
 
     const map = new Map();
-    const numberTree = new NumberTree(parentTree, this.rootDict.xref);
+    const numberTree = new NumberTree(parentTree, this.xref);
 
     if (Number.isInteger(id)) {
       const parentArray = numberTree.get(id);
       if (Array.isArray(parentArray)) {
         for (const ref of parentArray) {
           if (ref instanceof Ref) {
-            this.addNode(this.rootDict.xref.fetch(ref), map);
+            this.addNode(this.xref.fetch(ref), map);
           }
         }
       }
@@ -729,7 +728,7 @@ class StructTreePage {
     for (const [elemId, type] of ids) {
       const obj = numberTree.get(elemId);
       if (obj) {
-        const elem = this.addNode(this.rootDict.xref.fetchIfRef(obj), map);
+        const elem = this.addNode(this.xref.fetchIfRef(obj), map);
         if (
           elem?.kids?.length === 1 &&
           elem.kids[0].type === StructElementType.OBJECT

src/core/worker.js

@@ -558,7 +558,6 @@ class WorkerMessageHandler {
           } else if (
             await _structTreeRoot.canUpdateStructTree({
               pdfManager,
-              xref,
               newAnnotationsByPage,
             })
           ) {